1. Field of the Invention
The present invention relates generally to a fluid-filled elastic mount used as a vibration damper such as an automobile engine mount, which has a fluid chamber filled with a non-compressible fluid, and more particularly to such a fluid-filled elastic mount wherein the pressure of the fluid in the fluid chamber is suitably regulated to effectively change the damping characteristics of the mount, depending upon the type of the input vibrations received.
2. Discussion of the Prior Art
As a vibration damper for flexibly connecting two members in a vibration system or mounting one of the two members on the other member in a vibration damping fashion, there is known an elastic mount interposed between the two members of the vibration system. The elastic mount has an elastic body interposed between and elastically connecting a first and a second support which are respectively fixed to one and the other of the two members of the vibration system. This type of elastic mount may be used as an engine mount or a suspension bushing for a motor vehicle, for example.
Recently, there have been proposed various types of fluid-filled elastic mounts adapted to exhibit sophisticated damping characteristics, wherein the elastic body which elastically connects the first and second supports partially defines a fluid chamber filled with a non-compressible fluid. Some of these fluid-filled elastic mounts are adapted to electrically control the fluid pressure within the fluid chamber, depending upon the type of the input vibrations received, so that the specific vibrations can be suitably damped or isolated.
Examples of such electrically controllable fluid-filled elastic mount are disclosed in JP-A-60-8540, JP-A-59-1828 and JP-A-59-1829, wherein the fluid chamber is partially defined by an oscillating plate which consists of a magnetic body or a permanent magnet. The oscillating plate is actuated by a solenoid coil, so as to produce pressure pulsation within the fluid chamber to thereby control the fluid pressure within the chamber. Another type of electrically controllable fluid-filled elastic mount is disclosed in Publication No. 3-73741 of unexamined Japanese Utility Model Application, wherein the fluid chamber is partially defined by an oscillating plate fixed to one of an annular permanent magnet and an annular coil which is disposed radially inward or outward of and concentrically with the permanent magnet. The oscillating plate is oscillated by an electromagnetic force produced upon energization of the coil, so as to suitably control the fluid pressure within the fluid chamber.
In the fluid-filled elastic mount of the above type, the oscillating plate must be supported by the second support such that the plate is displaceable relative to the second support. In the known elastic mounts as disclosed in the above publications, therefore, the oscillating plate is supported by the second support with a suitable clearance therebetween, or connected at its outer peripheral portion to the second support through an elastic rubber layer.
In the former case where a suitable clearance is left between the oscillating plate and the second support, the fluid pressure in the fluid chamber tends to be reduced due to the flow of the fluid through the clearance. In the latter case where the elastic rubber layer is interposed between the oscillating plate and the second support, the fluid pressure in the fluid chamber tends to be reduced due to the expansive deformation of the elastic rubber layer. Consequently, the fluid pressure within the fluid chamber cannot be suitably and effectively regulated by the oscillation of the oscillating plate. Thus, the known fluid-filled elastic mount is incapable of exhibiting the intended damping characteristics depending upon the type of the input vibrations received.